Out-of-autoclave and alternative oven curing using a self heating tool

ABSTRACT

Method and apparatus for curing composite material to form composite structures are provided. A curing tool in one embodiment includes a curing tool that includes cured nano tube impregnated resin. At least two conductors are formed in the nano tube impregnated resin. The curing tool also includes a forming surface portion. The forming surface portion includes cured composite material of pre-preg material. The curing tool further includes at least a first insulation layer that separates the cured composite material from the nano tube impregnated resin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. patent applicationSer. No. 12/870,556 filed on Aug. 27, 2010, entitled the same as above,is herein incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The United States Government may have certain rights to this applicationunder contract No. FA9453-06-D0368-0003.

BACKGROUND

Composite structures formed from pre-impregnated (pre-preg) material areused in the formation of high strength-low weight structures such as,but not limited to, parts used to build aircraft and spacecraft.Pre-preg material is made of composite fibers such as carbon, glass,aramid and the like, that are bonded together with a resin that isactivated with heat to cure. The pre-preg material is typically suppliedin sheets or plies. The manufacturer then forms stacks of plies ofpre-preg material on a forming surface of a tool having a desired shape.Once the pre-preg material is formed on the tool, the tool is placed inan autoclave or conventional oven to cure the resin. The aerospaceindustry's desire for increasingly larger structures has resulted inlarger autoclaves and conventional ovens needed to cure the pre-pregmaterial. The larger the autoclaves and conventional ovens, the morecosts associated with building and operating them.

For the reasons stated above and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foran effective and efficient method of forming composite structureswithout the use of an autoclave or conventional oven.

SUMMARY OF INVENTION

The above-mentioned problems of current systems are addressed byembodiments of the present invention and will be understood by readingand studying the following specification. Embodiments of the presentinvention include both apparatuses and methods. The following summary ismade by way of example and not by way of limitation. It is merelyprovided to aid the reader in understanding some of the aspects of theinvention.

In one embodiment, a method of curing composite material to form acomposite structure is provided. The method including, laying up andforming pre-preg material on a forming surface of cured pre-pregmaterial of a composite structure forming tool and passing currentthrough nano tube impregnated resin within the forming tool to heat thetool internally to cure the pre-preg material.

In another embodiment, a curing tool is provided. The curing toolincludes cured nano tube impregnated resin. At least two conductors areformed in the nano tube impregnated resin. The curing tool also includesa forming surface portion. The forming surface portion includes curedcomposite material of pre-preg material. The curing tool furtherincludes at least a first insulation layer that separates the curedcomposite material from the nano tube impregnated resin.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more easily understood and furtheradvantages and uses thereof will be more readily apparent, whenconsidered in view of the detailed description and the following figuresin which:

FIG. 1 is a tool formation flow diagram of one embodiment of the presentinvention;

FIG. 2 is a partial side perspective view illustration of the formationof a support base portion of a tool of one embodiment of the presentinvention;

FIGS. 3A-3I are partial side perspective views illustrating the furtherformation of a heating tool of one embodiment of the present invention;

FIG. 3J is a bottom perspective view of the tool with formed passages ofone embodiment of the present invention;

FIG. 3K is a cross-sectional end view of a heating tool of oneembodiment of the present invention;

FIG. 3L is a cross section end view of the heating tool of FIG. 3Hcoupled to a controller and power source of one embodiment of thepresent invention;

FIG. 3M is a side perspective view of the forming of conductors in aheating tool of another embodiment of the present invention;

FIG. 4 is a composite structure forming flow diagram of one embodimentof the present invention;

FIG. 5A and 5B are partial side perspective views in forming a compositestructure on a self heated tool of one embodiment of the presentinvention; and

FIG. 6 is a side perspective view of a lay up of the heating tool ofanother embodiment; and

FIG. 7 is a tool formation flow diagram of the formation of the tool ofFIG. 6.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize specific features relevantto the present invention. Reference characters denote like elementsthroughout Figures and text.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that changesmay be made without departing from the spirit and scope of the presentinvention. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present invention isdefined only by the claims and equivalents thereof.

Embodiments of the present invention provide methods and apparatuses forfabricating molds, forms, or mandrels (that can be generally referred toas a tool) that are self heating. Hence, in embodiments, a tool isprovided that includes an internal heating source. Embodiments allowcomposite structures to be cured on the same tool as they werefabricated on without the need for an autoclave or an oven. Hence, largeout-of-autoclave structures are cured while sitting on a productionfloor thereby eliminating size constraints on autoclaves and ovens.Also, embodiments of the self heating tools allow for the massproduction of smaller composite parts. Rather than stacking hundreds ofuncured parts into an autoclave in a time-consuming process, each partcould have its own self heating tool. Each self heating tool can beheated on the production floor thereby providing an efficient part flowthrough the manufacturing plant.

In embodiments, a tool is formed with resin impregnated with nano tubes.The nano tubes in embodiments are electrically conductive. In oneembodiment the nano tubes used to impregnate the resin are carbonnanofibers (nano tubes). Passing current through the resin results inheat being generated due to electrical resistance in the nano tubeimpregnated resin. In embodiments, by varying the electrical power, theamount of heat created by the tool is varied. Moreover, in embodiments,conductive strips, such as, but not limited to, copper strips areembedded in the cured nano tube impregnated resin. An electricalpotential is created between adjacent conductive strips (conductivestrips that are near each other) which cause a current to pass throughthe nano tube impregnated resin. In an embodiment, an alternatingcurrent (AC) is applied to the adjacent conductive strips to produce thecurrent through the nano tube impregnated resin.

Referring to FIG. 1, a formation flow diagram 100 of one embodiment isillustrated. The formation flow diagram 100 is described below inconcert with illustrations in FIGS. 2 through 3I. In forming a tool, afirst step is determining what resin is compatible with a heat rangeneeded to cure pre-preg material (out of autoclave material) used toform a composite structure (102). Then it is determined what the nanotube percentage should be in relation to the resin (104). The percentageratio is based on a desired outcome (desired heat to be generated by atool). The nano tubes are then mixed with the resin to form carbon nanotube impregnated resin (106). A type of resin that can be used isK-factor resin provided by Boyce Components LLC. Example nano tubes usedare carbon nano tubes provided by Polygraf Products which is a part ofApplied Sciences Inc.

A foundation for the nano tube impregnated resin has to be provided toform the self heating tool. In one embodiment, plies of pre-pregmaterial 204 a, 204 b, 204 c are laid up and formed on a mandrel 202(108). The plies of pre-preg material form a support base portion 204.In one embodiment six to eight layers (plies) of carbon pre-pregmaterial are used to form the support base portion 204 which isapproximately 0.180 to 0.250 inches thick. FIG. 2 illustrates ply layers204 a, 204 b and 204 c being applied to the mandrel 202. In oneembodiment, the ply layers of pre-preg material 204 a, 204 b and 204 cinclude carbon fibers. The plies that make up the support base portion204 are then cured (110). After the support base portion 204 is cured, afirst insulation layer 300 is applied (112). This is illustrated in FIG.3A. In one embodiment, the first insulation layer 300 is a dry wovenglass layer 300 that is laminated on the support base portion 204. Theinsulation layer (dry woven glass layer 300) is then cured on thesupport base portion 204 (113). The thickness of the insulation layer300 in one embodiment is in the range of 0.003 to 0.005 inches.

Once the first dry woven glass layer 300 has been cured, a first coat ofcarbon nanotube impregnated resin 302 a is applied over the dry wovenglass layer 300 (114). This is illustrated in FIGS. 3B and 3C. In oneembodiment, a sponge brush 304 is used to apply the first coat of carbonnano tube impregnated resin 302 a to the first dry woven glass layer300. In one embodiment, the first coat of carbon nano tube impregnatedresin 302 a is applied with a uniform thickness of approximately 10 to11 mils. The desired spacing of the conductive strips 306 to be used inthe tool is then determined (116). In one embodiment, the conductivestrips 306 (conductors) are made of a metal such as copper. Theconductive strips 306 are then placed on a surface of the first coatcarbon nano tube impregnated resin 302 a (118) as illustrated in FIG.3D. A second coat of carbon nano tube impregnated resin 302 b is thenapplied over the first coat of carbon nano tube impregnated resin 302 aand the conductive strips 306 (120). The first and second coats ofcarbon nano tube impregnated resin 302 a and 302 b are then cured (122).The tool in this state is illustrated in FIG. 3F. Although, theconductive strips 306 are illustrated above as being substantiallystraight in the embodiment illustrated in FIGS. 3D and 3E, in otherembodiments, the conductive strips 306 a can take any shape as needed todistribute the heat in the tool 350 as desired. For example, in FIG. 3Mthe conductive strips 306 a and 306 b are patterned to achieve a desiredheating distribution.

A second insulation layer 310 is laminated then laid up and laminated onthe carbon nano tube impregnated resin 302 b (124). This layer of theinsulation 310 is then cured (125). In one embodiment, the secondinsulation layer 310 is a dry woven glass layer 310 having a thicknessin the range of 0.003 to 0.005 inches. The addition of the secondinsulation layer 310 is illustrated in FIG. 3G. Once the secondinsulation layer 310 has been formed, ply layers 312 a and 312 b ofpre-preg material are laid up (126) and cured (126) to form a toolforming surface 312 of the tool 350. The lying up of the ply layers 312a and 312 b are illustrated in FIG. 3H and the formed tool formingsurface 312 is illustrated in FIG. 3I. FIG. 3I also illustrates thelayers of a formed tool 350 in an embodiment. In one embodiment, the plylayers of pre-preg material 312 a and 312 b include carbon fibers.Moreover, the number of ply layers 312 a and 312 b used to form the toolforming surface portion 312 can vary depending on a desired outcome. Inone embodiment, the thickness of the tool forming surface 312 is in arange of 0.035 to 0.040 inches. Although, the formed tool 350illustrated in FIG. 3I is generally C-shaped, the tool can have anydesired cross-sectional shape desired depending on the application.Moreover, the tool can be straight along its length, it can be curvedalong its length and its cross-sectional geometry can vary along itslength. Hence, any shaped tool is contemplated and tool 350 of FIG. 3Iis merely an example of one shape of a tool used to form a C-shapedcomposite structure.

In one embodiment, the tool 350 is removed from the base mold 124 oncethe tool is formed. Bores 330 are then selectively formed through thebase support portion 204, the first insulation layer 300 and the firstcured carbon nano tube impregnated resin 302 a to the conducting strips306 (130). This is illustrated in FIG. 3J and FIG. 3K. In oneembodiment, a Dremel® power tool by the Robert Bosch Tool Corporation,or similar tool, is used to make the bores through the tool 350 to therespective conducting strips 306. Conductive wires 340 are then coupledto the conductive strips 306 (132) as illustrated in FIG. 3L. FIG. 3Lfurther illustrates, a power source 342 coupled to the conductive wires340 and a controller 344. The controller 344 is designed to control thepower source 342. As stated above, in one embodiment, the power source342 provides an alternating current (AC) to respective conductive strips306 to heat up the tool 350. As illustrated in FIG. 3L, the first andsecond insulation layers 300 and 310 insulate the conductors 306 andnano tube impregnated resin 302 a from the material that makes up thesupport base portion 204 and the tool forming surface portion 312. Thisprevents the support base portion 204 and the tool forming surfaceportion 312 from passing current out of the tool 350. This would be anissue in an embodiment where the support base portion 204 and the toolforming surface 312 include conductive material such as carbon fibers.The insulation layers 300 and 310 also help prevent the nano tubeimpregnated resin from spreading onto the composite material of thesupport base portion 204 and the tool forming surface portion 312 duringformation of the tool.

Referring to FIG. 4, an illustration of a composite structure formingflow diagram 400 is illustrated. The flow diagram 400 is described inconcert with FIGS. 5A and 5B. The process starts by laying up andforming pre-preg material on the tool (402). In one embodiment, this isdone by applying one or more layers of pre-preg material on the toolforming surface portion 312 of the tool 350 and pressing the one or morelayers of pre-preg material onto the tool forming surface portion 312 ofthe tool 350 to form the pre-preg material into the shape of the toolforming surface portion 312. An example of laying up a layer of plymaterial 500 on a tool 350 is illustrated in FIG. 5A. Any method knownin the art to lay up and form the pre-preg material 500 on the tool 350can be used. An example method of laying up and forming pre-pregmaterial on a tool is illustrated in commonly assigned U.S. Pat. No.7,249,943 entitled “Apparatus for Forming Composite Stiffeners andReinforced Structures” that issued on Jul. 31, 2007 and U.S. Pat. No.7,513,769 entitled “Apparatus and Methods for Forming CompositeStiffeners and Reinforcing Structures” that issued on Apr. 7, 2009 bothof which are incorporated herein by reference. Moreover, any othermethod of laying up and forming the pre-preg material on a tool can beused, such as hot drape forming and other methods known in the art. Oncethe pre-preg material is positioned on the tool, the power source 342provides power to the conductive strips 306 in the tool 350 (404). Anexample, of the power source 342 coupled to heat a tool 350 isillustrated in FIG. 5B. In FIG. 5B pre-preg material on the tool 350 iscured to form a composite structure 550. In particular, the heat of thetool 350, as a result of the power being supplied to conductors(conductive strips) in the tool 350, cures the pre-preg material (404)to form the composite structure 550. In one embodiment, a vacuum bagsystem known in the art is used to compact the pre-preg material duringcuring (403). Once the pre-preg material is cured, the formed compositestructure 550 is removed from the tool 350 (406).

Referring to FIG. 6, a lay up (formation) of the tool 350 of anotherembodiment is illustrated. In this embodiment the tool is formed on amaster 602 (mandrel) in an opposite manner as the embodiment discussedabove. In this embodiment, the master 602 is generally in the shape ofthe part to be made on the heated tool 305. Hence, the formation of thetool on a mandrel can be made in different ways. One advantage to theformation of the tool 350 as illustrated in FIG. 6 is that the toolforming surface portion 312 will be relatively smooth and provide a goodsurface on which to form the composite structures. Conversely, a surfaceof the support base portion 102 will be rougher due to the use of one ormore vacuum bags used to cure the tool 350.

FIG. 7 illustrated a tool formation flow diagram 700 pursuant to the layup illustrated in FIG. 6. The flow diagram 700 starts similar to theflow diagram 100 described above. The resin is selected (102). The nanotube percentage is selected (104). The nano tubes and resin are mixed toform the nano tube impregnated resin 302 (106). Plies of pre-pregmaterial are layed up on the master (708). The plies are then cured(710) to form the tool forming surface portion 312 on a surface of themaster 702. A first insulation layer 300 is then laminated on a backside of the tool forming surface portion 312 (712). The first insulationlayer 300 is then cured (713). A first coat of nano tube resin 302 a isthen applied to the cured first insulation layer 300 (714). It is thendetermined what the spacing should be for the conductive strips (716).The conductive strips 306 are then placed on the first coat of nano tuberesin 302 a (718). A second coat of nano tube resin 302 b is thenapplied covering the conductive strips 306 (720). The nano tube resin302 a and 320 b is then cured (722). A second layer of insulation 310 isthen laminated over the nano tube resin 302 a and 320 b (724). Theinsulation layer 310 is then cured (725). Plies of pre-preg material arethen layed up on the second layer of insulation 310 (726). The plies ofpre-preg material are then cured to form the support base portion (128).Bores are then formed through the support base portion 204 to theconductive strips (130) as described above in regards to FIG. 3J.Conductive wires are then coupled to the conductive strips (132). Asunderstood in the art, curing of the various materials to make the tool350 may include various forms of vacuum bagging techniques.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiment shown. This applicationis intended to cover any adaptations or variations of the presentinvention. Therefore, it is manifestly intended that this invention belimited only by the claims and the equivalents thereof.

1. A method of curing composite material to form a composite structure,the method comprising: laying up and forming pre-preg material on aforming surface of cured pre-preg material of a composite structureforming tool; and passing current through nano tube impregnated resinwithin the forming tool to heat the tool internally to cure the pre-pregmaterial.
 2. The method of claim 1, wherein laying up and formingpre-preg material further comprises: applying and pressing the pre-pregmaterial on the forming surface of the forming tool.
 3. The method ofclaim 1, wherein passing current through the nano tubes in the toolfurther comprises: creating a voltage potential between adjacentconductive strips in the tool.
 4. The method of claim 3, whereincreating the voltage potential between adjacent conductive stripsfurther comprises: coupling alternating current to the conductivestrips.
 5. A curing tool comprising: cured nano tube impregnated resin;at least two conductors formed in the nano tube impregnated resin; aforming surface portion including cured composite material of pre-pregmaterial; and at least a first insulation layer separating the curedcomposite material from the nano tube impregnated resin.
 6. The curingtool of claim 5, further comprising: a support base portion of curedcomposite material; and at least one second insulation layer separatingthe support base portion of the cured composite material from the curednano tube impregnated resin.
 7. The curing tool of claim 6, wherein atleast one of the first and second insulation layers is a layer of curedglass ply.
 8. The curing tool of claim 6, further comprising: thesupport base portion, the at least second insulation layer and a portionof the cured nano tube impregnated resin have aligned passages to the atleast two conductors; and a conductive wire for each aligned passage,each conductive wire passing through associated aligned passages, eachconductive wire coupled to an associated conductor.
 9. The curing toolof claim 8, further comprising: a power supply coupled to the pluralityof conductive wires; and a controller configured to control the powersupply.
 10. The curing tool of claim 9, wherein the controller isconfigured to vary the power of the power supply to adjust heat producedby the curing tool.
 11. The curing tool of claim 9, wherein the powersupply supplies an alternating current.
 12. The curing tool of claim 5,wherein the at least two conductors are conductive strips positionedrelatively parallel to each other and spaced select distances apart.